Method for generating catalysts

ABSTRACT

A process is provided for the regeneration of a heterogeneous catalyst used for the preparation of compounds containing NH 2  groups by the hydrogenation, with hydrogen, of compounds containing at least one unsaturated carbon-nitrogen bond, wherein  
     a) the feed of the compound to be hydrogenated is stopped and  
     b) the heterogeneous catalyst is treated with a compound of the formula 
     R 1 R 2 N—CO—R 3   (I), 
      in which  
     R 1  is hydrogen or C 1 -C 4  alkyl and  
     R 2 , R 3  independently of one another are each hydrogen or C 1 -C 4  alkyl or together are a C 3 -C 6  alkylene group,  
     or mixtures of such compounds, at a pressure ranging from 0.1 to 30 MPa and a temperature ranging from 100 to 300° C., with the proviso that the compound of formula (I) is in liquid form during the treatment.

[0001] The present invention relates to a process for the regenerationof a heterogeneous catalyst used for the preparation of compoundscontaining NH₂ groups by the hydrogenation, with hydrogen, of compoundscontaining at least one unsaturated carbon-nitrogen bond, wherein

[0002] a) the feed of the compound to be hydrogenated is stopped and

[0003] b) the heterogeneous catalyst is treated with a compound offormula

R¹R²N—CO—R³  (I),

[0004]  in which

[0005] R¹ is hydrogen or C₁-C₄ alkyl and

[0006] R², R³ independently of one another are each hydrogen or C₁-C₄alkyl or together are a C₃-C₆ alkylene group,

[0007] or mixtures of such compounds, at a pressure ranging from 0.1 to30 MPa and a temperature ranging from 100 to 300° C., with the provisothat the compound of formula (I) is in liquid form during the treatment.

[0008] Processes for the preparation of compounds containing NH₂ groupsby the hydrogenation, with hydrogen, of compounds containing at leastone unsaturated carbon-nitrogen bond, in the presence of a heterogeneouscatalyst, are generally known, for example from Houben-weyl, Vol. 11/1(Nitrogen Compounds II, Amines), pp. 545-574, 4th edition, 1957.

[0009] WO 97/37963, WO 97/37964, WO 98/04515 and DE-A-198 09 688disclose processes for the hydrogenation of adipodinitrile tohexamethylenediamine, or mixtures containing 6-aminocapronitrile andhexamethylenediamine, in the presence of heterogeneous catalysts basedon iron, cobalt or nickel or compounds thereof. In such processes,relevant catalyst properties, such as activity or selectivity,deteriorate with operating time.

[0010] Although a drop in activity can be compensated by raising thereaction temperature, the disadvantage here is that the selectivity of acatalyst conventionally decreases with increasing reaction temperatureand, in addition, the higher temperature accelerates the further drop inactivity.

[0011] Processes are known for the regeneration of a catalyst whoserelevant properties, such as activity or selectivity, have deterioratedwith operating time. Regeneration is understood here as meaning aprocess by which said catalyst properties can be improved again. Thus WO97/37963, WO 97/37964 and WO 98/04515 describe processes for theregeneration of a heterogeneous catalyst (whose activity and selectivityhave dropped) used for the preparation of compounds containing NH₂groups by the hydrogenation, with hydrogen, of compounds containing atleast one unsaturated carbon-nitrogen bond, by treatment with hydrogenunder defined process conditions.

[0012] Although these regeneration processes give a good result in termsof improving the selectivity and activity, it would be desirable toprotect the catalyst by reducing the temperature and time required forthe regeneration.

[0013] It is an object of the present invention to provide a process forthe regeneration of a heterogeneous catalyst used for the preparation ofcompounds containing NH₂ groups by the hydrogenation, with hydrogen, ofcompounds containing at least one unsaturated carbon-nitrogen bond, saidprocess affording the regeneration in a technically simple and economicmanner while avoiding said disadvantages.

[0014] We have found that this object is achieved by the process definedat the outset.

[0015] The heterogeneous catalysts to be regenerated have previouslybeen used for the preparation of compounds containing NH₂ groups by thehydrogenation, with hydrogen, of compounds containing at least oneunsaturated carbon-nitrogen bond.

[0016] As compounds [lacuna] at least one unsaturated carbon-nitrogenbond such as a carbon-nitrogen double or triple bond, it is preferred touse a C₄-C₈ alkyl nitrile or dinitrile or mixtures of such nitrites ordinitriles, such as butane nitrile, pentane nitrile, hexane nitrile,heptane nitrile, octane nitrile, butane dinitrile, pentane dinitrile,hexane dinitrile, heptane dinitrile and octane dinitrile, particularlypreferably terminal C₄-C₈ dinitriles such as 1,4-dicyanobutane(“adipodinitrile”), 1,5-dicyanopentane, 1,6-dicyanohexane,1,7-dicyanoheptane and 1,8-dicyanooctane, C₅-C₈ cycloalkyl nitrites ordinitriles such as cyclopentyl nitrile, cyclohexyl nitrile, cycloheptylnitrile, cyclooctyl nitrile, cyclopentyl dinitrile, cyclohexyldinitrile, cycloheptyl dinitrile and cyclooctyl dinitrile, or aminonitrites containing from 4 to 8 carbon atoms, preferablyalpha,omega-amino nitrites such as 5-aminovaleronitrile and6-aminocapronitrile.

[0017] The nitrites, dinitriles and amino nitrites can also carry otherfunctional groups provided that they do not detract from thehydrogenation or that simultaneous or partial hydrogenation is desired.Examples which may be mentioned are C₁-C₄ alkyl groups, aryl groups,especially phenyl, C₅-C₈ cycloalkyl, aminoalkyl, N-alkylaminoalkyl,N-(cyanomethyl)aminoalkyl and the imino group (C═NH, C═NR), preferablythe imino group.

[0018] Adipodinitrile, 6-aminocapronitrile,3-cyano-3,5,5-trimethylcyclohexylimine, NC—(CH₂)₂—NH—(CH₂)₂—CN,NC—(CH₂)₂—NH—(CH₂)₂—NH—(CH₂)₂—CN and 1-cyano-2-aminoethane areespecially suitable, adipodinitrile being particularly preferred.

[0019] In one advantageous embodiment, adipodinitrile can behydrogenated to hexamethylenediamine.

[0020] In another advantageous embodiment, adipodinitrile can behydrogenated to a mixture containing hexamethylenediamine and6-aminocapronitrile.

[0021] On the basis of previous observations in respect of thecatalytically active component, suitable heterogeneous catalysts to beregenerated are any heterogeneous catalysts known for the preparation ofcompounds containing NH₂ groups by the hydrogenation, with hydrogen, ofcompounds containing at least one unsaturated carbon-nitrogen bond.

[0022] In one preferred embodiment, it is possible to use aheterogeneous catalyst containing, as the catalytically activecomponent, an element selected from the group consisting of iron, cobaltand nickel or mixtures thereof, particularly preferably iron or cobaltor mixtures thereof, and very particularly preferably iron.

[0023] In another preferred embodiment, it is possible to use aheterogeneous catalyst containing, as the catalytically activecomponent, a compound of an element selected from the group consistingof iron, cobalt and nickel or mixtures thereof, particularly preferablyiron or cobalt or mixtures thereof, and very particularly preferablyiron.

[0024] Such catalysts can be used unsupported, especially for fixed bedor suspension methods, for example in the form of Raney catalysts orother unsupported forms (so-called unsupported catalysts). Theunsupported forms can contain small amounts of auxiliary substancescompared with the high content of active component. These auxiliarysubstances can have favorable effects either on the catalytic activityand/or selectivity or on the catalyst properties such as hardness,abrasion or chemical or thermal stability. The total amount of auxiliarysubstances generally ranges from 0 to 20% by weight, based on the amountof active component. Auxiliary substances which can be used are oxides,phosphates and sulfates of alkali metal and alkaline earth metalcompounds, thermally stable oxides such as silicon dioxide, aluminumoxide, titanium dioxide and zirconium dioxide, and other transitionmetal oxides. It is also possible to use supported catalysts. Suitablesupports are generally ceramic supports such as aluminum oxide, silicondioxide, titanium dioxide and zirconium dioxide, or silicon carbide oractivated carbon. In supported catalysts, the content of activecomponent normally ranges from 3 to 95% by weight, preferably from 30 to95% by weight, based on the support.

[0025] If desired, the catalysts can also be modified with metals ofgroup VIB (Cr, Mo, W) and group VIII (Ru, Os, Rh, Ir, Pd, Pt) of thePeriodic Table of the Elements, and with copper, manganese and rhenium,the content of the non-modifying part of the active component generallyranging from 50 to 99.9% by weight, preferably from 80 to 99% by weight,based on the whole active component.

[0026] Furthermore, the catalysts can be modified with a compound basedon an alkali metal or alkaline earth metal such as lithium, sodium,potassium, rubidium, cesium, magnesium, calcium, strontium or barium.The chosen weight ratio conventionally ranges from 0 to 5% by weight,preferably from 0.1 to 3% by weight, of alkali metal or alkaline earthmetal, based on the non-modifying part of the active component.

[0027] Furthermore, in the case of catalysts whose active component are[sic] based on iron or an iron compound, the catalysts can be modifiedwith a compound based on 1, 2, 3, 4 or 5 elements selected from thegroup consisting of aluminum, silicon, zirconium, titanium and vanadium.The chosen weight ratio is conventionally 0 to 3% by weight of modifyingagent, based on the iron.

[0028] Furthermore, in the case of catalysts whose active component are[sic] based on iron or an iron compound, the catalysts can be modifiedwith a compound based on manganese. The chosen manganese concentrationis conventionally 0 to 25% by weight, preferably 0.01 to 5% by weight,based on the iron.

[0029] Such catalysts and their preparation are known per se, forexample from WO 97/37963, WO 97/37964, WO 98/04515 and DE-A-198 09 688.

[0030] Before being used, the catalysts can be activated, for example bytreatment with hydrogen, the activation being carried out in a mannerknown per se under atmospheric pressure or superatmospheric pressure andat temperatures above 200° C.

[0031] The hydrogenation can be carried out by the liquid phase, trickleor suspension method.

[0032] If the hydrogenation is carried out in suspension, the chosentemperatures conventionally range from 40 to 150° C., preferably from 50to 100° C. and particularly preferably from 60 to 90° C.; the chosenpressure generally ranges from 2 to 20 MPa, preferably from 3 to 10 MPaand particularly preferably from 4 to 9 MPa. The residence times dependessentially on the desired yield and selectivity and the desiredconversion; the residence time is conventionally chosen so as to achievethe maximum yield, ranging for example from 50 to 275 min, preferablyfrom 70 to 200 min.

[0033] In the suspension method, a liquid diluent can also be added,suitable liquid diluents preferably being ammonia, amines, diamines andtriamines having from 1 to 12 carbon atoms, such as trimethylamine,triethylamine, tripropylamine or tributylamine, or alcohols, especiallymethanol or ethanol; ammonia is particularly preferred. The chosenconcentration of compound to be hydrogenated ranges appropriately from10 to 90% by weight, preferably from 30 to 80% by weight andparticularly preferably from 40 to 70% by weight, based on the sum ofcompound to be hydrogenated and liquid diluent.

[0034] The chosen amount of catalyst generally ranges from 1 to 50% byweight, preferably from 5 to 20% by weight, based on the amount ofcompound to be hydrogenated.

[0035] The suspension hydrogenation can be carried out batchwise orcontinuously, preferably continuously, and normally in the liquid phase.

[0036] The hydrogenation can also be carried out batchwise orcontinuously, preferably continuously, in a fixed bed reactor by thetrickle or liquid phase method, the chosen temperature conventionallyranging from 30 to 200° C., preferably from 50 to 150° C., and thechosen pressure normally ranging from 2 to 30 MPa, preferably from 3 to20 MPa. The hydrogenation is preferably carried out in the presence of aliquid diluent, preferably ammonia, amines, diamines and triamineshaving from 1 to 12 carbon atoms, such as trimethylamine, triethylamine,tripropylamine or tributylamine, or alcohols, especially methanol orethanol, and particularly preferably ammonia.

[0037] In one preferred embodiment, the chosen ammonia content rangesfrom 0.5 to 10 g, preferably from 1 to 6 g, per gram of compound to behydrogenated, especially adipodinitrile.

[0038] Preferably, the chosen catalyst loading ranges from 0.1 to 2.0kg, preferably from 0.3 to 1.0 kg, of compound to be hydrogenated/l×h,especially adipodinitrile/l×h. Here again, the conversion and hence theselectivity can be specifically adjusted by changing the residence time.

[0039] The hydrogenation can be carried out in a conventional reactorsuitable for this purpose.

[0040] If the reaction is carried out in the gas phase, the chosentemperatures conventionally range from 100 to 250° C., preferably from160 to 200° C.; the chosen pressure generally ranges from 0.01 to 3 MPa,preferably from 0.09 to 0.5 MPa. Also, the amount of hydrogen used isnormally 2 to 300 mol, preferably 10 to 200 mol, per mol of compoundcontaining at least one unsaturated carbon-nitrogen bond.

[0041] In one preferred embodiment, the hydrogenation of the compound tobe hydrogenated, especially adipodinitrile, is carried out in thepresence of ammonia as the liquid diluent with fixed bed catalysts.

[0042] The catalyst is regenerated by first stopping the feed ofcompound to be hydrogenated, especially adipodinitrile, and the feed ofliquid diluent, if used. The catalyst and the reaction mixture canadvantageously be separated.

[0043] The hydrogen feed can also be stopped, the catalystadvantageously being regenerated in the presence of hydrogen. Accordingto the invention, the catalyst to be regenerated is treated with acompound of formula (I):

R¹R²N—CO—R³  (I),

[0044] or mixtures of such compounds.

[0045] In this formula, R¹ is hydrogen or a C₁-C₄ alkyl such as methyl,ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl or t-butyl,preferably hydrogen or methyl.

[0046] R², R³ independently of one another are each hydrogen or C₁-C₄alkyl such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl,s-butyl or t-butyl, preferably hydrogen or methyl, or together are aC₃-C₆ alkylene group of the type —(CH₂)_(n)—, in which n can take avalue of 3, 4, 5 or 6, preferably 3.

[0047] In the case where they are not hydrogen, the groups R¹, R² and R³can be substituents such as aryl groups, especially phenyl, C₅-C₈cycloalkyl, aminoalkyl and, if the group R¹, R² or R³ in question is notmethyl, C₁-C₄ alkyl groups.

[0048] In the case where they are not hydrogen, the groups R¹, R² and R³can carry functional groups such as halogens, for example fluorine,chlorine or bromine.

[0049] The groups R¹, R² and R³ preferably carry no functional groups.

[0050] In one preferred embodiment, R² and R³ together are a C₃ alkylenegroup of the type —(CH₂)₃—.

[0051] In another preferred embodiment, R² and R³ together are a C₃alkylene group of the type —(CH₂)₃— and R¹ is a methyl group.

[0052] In another preferred embodiment, R¹ and R² are each a methylgroup and R³ is hydrogen.

[0053] According to the invention, the heterogeneous catalyst is treatedwith a compound of formula (I) with the proviso that said compound is inliquid form during the treatment.

[0054] Treatment is understood as meaning the batchwise or continuouscontacting of the catalyst with a compound of formula (I).

[0055] If the catalyst is a suspension catalyst, it can advantageouslybe suspended in a compound of formula (I), which can be introduced intothe catalyst continuously or batchwise. The compound of formula (I) canbe separated from the catalyst continuously or batchwise.

[0056] If the catalyst is a fixed bed catalyst, it can be removed fromthe reactor prior to regeneration. In one advantageous embodiment, theregeneration can be effected in the hydrogenation reactor withoutremoving the catalyst.

[0057] If the catalyst is a fixed bed catalyst, a compound of formula(I) can advantageously be passed through it continuously or batchwise.The compound of formula (I) can be introduced into the catalystcontinuously or batchwise and can be separated from the catalystcontinuously or batchwise.

[0058] The compound of formula (I) separated from the catalyst can bediscarded or, advantageously, recycled into the catalyst, optionallyafter purification.

[0059] According to the invention, the regeneration is effected at apressure ranging from 0.1 to 30 MPa. If this is done in the presence ofhydrogen, the regeneration can advantageously be effected at thepressure previously applied during the hydrogenation. If theregeneration is continuous, the appropriate amount of hydrogenadvantageously ranges from 1 to 100 g, preferably from 2 to 50 g, ofhydrogen/l of reactor volume×hour.

[0060] The regeneration can be effected at temperatures of at least 100°C., preferably of at least 120° C., particularly preferably of at least140° C. and very particularly preferably of at least 160° C.

[0061] The appropriate upper temperature limit for the regeneration isthe decomposition point of the compound of formula (I), i.e. generally300° C., and is preferably at most 200° C. and particularly preferablyat most 180° C.

[0062] The duration of treatment of the catalyst to be regenerated isgenerally 1 to 12 hours, preferably 2 to 4 hours.

[0063] After the treatment, the regenerated catalyst and the compound offormula (I) are separated from one another. The regenerated catalyst canthen be re-used, like a freshly prepared catalyst, in a process for thepreparation of compounds containing NH₂ groups by the hydrogenation,with hydrogen, of compounds containing at least one unsaturatedcarbon-nitrogen bond.

EXAMPLES Example 1

[0064] Three tubular reactors connected in series (total length=4.5 m,d=6 mm) were filled with 142 ml (240 g) of an iron-based catalystprepared according to Example 1a of DE-A-198 09 688 (1.5 to 3 mm chips),which was then reduced in a stream of hydrogen (200 l/h) underatmospheric pressure, the temperature being raised from 70° C. to 340°C. over 24 hours and then kept at 340° C. for 72 hours.

[0065] After the temperature had dropped, a mixture of 0.66 mol/h ofadipodinitrile, 365 ml/h of ammonia and 1.05 mol/h of hydrogen wasintroduced into the reactor. The reactor temperature was adjusted sothat the total selectivity in respect of 6-aminocapronitrile andhexamethylenediamine was constant at a pressure of 25 MPa. This was doneby setting the temperature at 94° C. initially and raising it to 107° C.over 9000 hours.

[0066] The feeds were then stopped and the catalyst was flushed for fourhours at 160° C. with 100 ml/h of N-methyl-alpha-pyrrolidone.

[0067] It was then flushed for four hours at 107° C. with 365 ml/h ofammonia, after which the original feeds were restarted. The reactortemperature could be lowered to 94° C. in order to achieve the totalselectivity obtained prior to regeneration.

Example 2

[0068] In a continuously operated tubular reactor, adipodinitrile washydrogenated to a mixture of 6-aminocapronitrile andhexamethylenediamine at 70 bar and at a loading of 0.22 kg/l×h ofCr-doped Raney Co chips having a size of 1-3 mm, in the presence ofammonia as solvent.

[0069] After an operating time of 80 h, the adipodinitrile conversionwas 92.8% at a mean temperature of 37.0° C. over the length of thereactor.

[0070] After an operating time of 2004 h, the catalyst had continuouslylost activity to give an adipodinitrile conversion of only 59.9% at amean temperature of 48.5° C. over the length of the reactor.

[0071] The catalyst was regenerated by stopping the feeds ofadipodinitrile and ammonia and flushing the catalyst for 4 hours withN-methyl-alpha-pyrrolidone at a loading of 2 kg/l×h and at 150° C., thehydrogen feed being maintained at 500 Nl/l×h and the pressure beingmaintained at 70 bar. After the regeneration, the reactor was cooled andstarted up again as with a fresh catalyst.

[0072] After a total operating time of 2112 h, the adipodinitrileconversion was 91.4% and the initial total selectivity in respect of6-aminocapronitrile and hexamethylenediamine was achieved at a meantemperature of 37.3° C. over the length of the reactor.

We claim:
 1. A process for the regeneration of a heterogeneous catalystused for the preparation of compounds containing NH₂ groups by thehydrogenation, with hydrogen, of compounds containing at least oneunsaturated carbon-nitrogen bond, wherein a) the feed of the compound tobe hydrogenated is stopped and b) the heterogeneous catalyst is treatedwith a compound of formula (I): R¹R²N—CO—R³  (I),  in which R¹ ishydrogen or C₁-C₄ alkyl and R², R³ independently of one another are eachhydrogen or C₁-C₄ alkyl or together are a C₃-C₆ alkylene group, ormixtures of such compounds, at a pressure ranging from 0.1 to 30 mpa anda temperature ranging from 100 to 300° C., with the proviso that thecompound of formula (I) is in liquid form during the treatment.
 2. Aprocess as claimed in claim 1 wherein the heterogeneous catalystregenerated has been used for the hydrogenation of adipodinitrile.
 3. Aprocess as claimed in claim 1 wherein the heterogeneous catalystregenerated has been used for the hydrogenation of adipodinitrile tohexamethylenediamine.
 4. A process as claimed in claim 1 wherein theheterogeneous catalyst regenerated has been used for the hydrogenationof adipodinitrile to a mixture containing hexamethylenediamine and6-aminocapronitrile.
 5. A process as claimed in any of claims 1 to 4wherein, in formula (I), R² and R³ together form a C₃ alkylene group. 6.A process as claimed in any of claims 1 to 4 wherein, in formula (I), R²and R³ together are a C₃ alkylene group and R¹ is a methyl group.
 7. Aprocess as claimed in any of claims 1 to 6 wherein, in formula (I), R¹and R² are each a methyl group and R³ is hydrogen.
 8. A process asclaimed in any of claims 1 to 7 wherein the heterogeneous catalystcontains, as the catalytically active component, an element selectedfrom the group consisting of iron, cobalt and nickel or mixturesthereof.
 9. A process as claimed in any of claims 1 to 7 wherein theheterogeneous catalyst contains, as the catalytically active component,a compound. of an element selected from the group consisting of iron,cobalt and nickel or mixtures thereof.
 10. A process as claimed in anyof claims 1 to 9 wherein the regeneration is effected in the presence ofhydrogen.
 11. A process as claimed in any of claims 1 to 9 wherein thehydrogen feed is stopped in step a).